In a phase III clinical trial, a single oral dose of norastemizole (25 mg oral) was shown to significantly attenuate the histamine-induced wheal and flare response within 30 minutes.

HEK-293 cells stably transfected with the human ether-a go-go-related gene (HERG) K+ channel were cultured in minimal essential medium supplemented with 10% fetal bovine serum and 400 micro-g/mL G418. Norastemizole was dissolved in absolute ethanol and diluted to experimental concentrations with extracellular HEPES-buffered in Tyrode's solution. Cell voltage was recorded under steady-state drug block conditions at several concentrations of norastemizole. Norastemizole was observed to block the HERG current, but required higher concentrations and produced an incomplete block relative to comparator compounds. Norastemizole was estimated to have an IC50 of 27.7 nM and a maximum HERG current block of 48%.